Field of the Invention
This invention relates generally to a toothed power transmission belt, more particularly to a toothed belt with a heat and wear resistant fabric for tooth support, and specifically to a toothed belt with tooth support fabric including fibers of poly p-phenylene sulfide.
Description of the Prior Art
Toothed power transmission belts are used in synchronous belt drives. Toothed belts commonly have an elastomeric body with a layer of reinforcing tensile cords which provide high dimensional stability. The body under the cord layer is formed into a series of teeth which mesh in pulleys or sprockets and transmit drive loads to the tensile cord. The teeth are commonly covered with a reinforcing fabric such as a woven stretch fabric of nylon-66 multi-filament yarns. Tooth reinforcing fabrics may be of plain or twill weave or the like. Fabric layers may also be used on the backside of toothed belts, on the backside or pulley contacting profile of multi-v-ribbed belts, or in v-belts or flat belts. Nylon-66 (also known as polyamide-66 or PA-66) fabrics commonly utilize textured or crimped yarns in one direction, as described for example in U.S. Pat. No. 4,826,472 which is hereby incorporated herein by reference, to allow sufficient stretch in the longitudinal direction of the belt to conform to the teeth during a flow-through belt manufacturing process, as described for example in U.S. Pat. No. 3,078,206 which is hereby incorporated herein by reference. Other fabrics utilize elastic core yarns to achieve sufficient stretch in the longitudinal direction, as described for example in U.S. Pat. No. 5,529,545 which is hereby incorporated herein by reference. These yarns will be called hereinafter the “longitudinal yarns” of the belt lengthwise direction, whereas the yarns to be combined with the longitudinal yarns will be called the “transverse yarns”. However, these “longitudinal yarns” and “transverse yarns” are not necessarily coincident with the terminology “warp” and “weft”, as used to describe the textile structure.
Increased demands on power transmission belts, particularly in the area of automotive under-hood applications, have lead to a number of fabric variations intended to improve the performance of power transmission belts, including for example, use or substitution of para-aramid, meta-aramid, polyetheretherketone (PEEK), polyimide (PI), or polytetrafluoroethylene (PTFE) yarns or fibers in place of some or all of the usual nylon weft yarns or fibers, for example as disclosed in WO 2006-066669. Each proposed variation has limitations, so new fabric alternatives are yet desirable. One problem is that PEEK, aramid, and PTFE are not as easily bonded to elastomer belt body compositions as nylon is, so only limited amounts of substitution for nylon in the weft are practical such as disclosed in WO 2006-066669. Another problem is that para-aramid cannot be textured like nylon, so other means of imparting stretch to some longitudinal yarns must be used, such as combining aramid with elastic yarn as described for example in U.S. Pat. No. 5,529,545. Such combined yarns may suffer from decreased properties. Many such high-performance yarns and fabrics may be limited in use by economic considerations.
What is needed is a stretch fabric for power transmission belts having high heat, fluid, flex, and abrasion resistance, but at a much more reasonable cost than other proposed solutions. What is needed is a fabric which can be processed like conventional nylon-66 stretch fabrics. What is needed is a fabric with good adhesion to elastomeric materials used in belts. The present invention meets one or more of these needs.